A hydrocarbon resource may be particularly valuable as a fuel, for example, gasoline. One particular hydrocarbon resource, bitumen, may be used as a basis for making synthetic crude oil (upgrading), which may then be refined into gasoline.
One technique for recovering a hydrocarbon resource may be the steam assisted gravity drainage (SAGD) process. In the SAGD process, two parallel horizontal oil wells are drilled in a subterranean formation, one about 4 to 6 meters above the other. The upper well injects steam, possibly mixed with solvents, and the lower one collects the heated crude oil or bitumen that flows out of the subterranean formation, along with any water from the condensation of injected steam. The basis of the process is that the injected steam forms a “steam chamber” that grows vertically and horizontally in the subterranean formation.
The heat from the steam reduces the viscosity of the heavy crude oil or bitumen, which allows it to flow down into the lower wellbore. The steam and gases rise because of their low density compared to the heavy crude oil below so that steam is not produced at the lower production well. Oil and water flow is by a countercurrent, gravity driven drainage into the lower well bore. The condensed water and crude oil or bitumen is recovered to above the subterranean formation by pumps.
In some instances, a wormhole may form in an undesirable location in the subterranean formation between the upper and lower wellbores. The wormhole may reduce the amount of the hydrocarbon resource recovered, and/or may reduced efficiency of the hydrocarbon recover process. Accordingly, it may be desirable to map a wormhole in the subterranean formation, for example, for the purposes of repair.
One technique for mapping a wormhole may include using a global positioning system (GPS) tracking device to be inserted into the one of the upper and lower wellbore. However, the GPS tracking device may not provide accurate position information underground as ultra-high frequency (UHF), 1575 Mhz GPS signals generally do not penetrate or reach into the subterranean formation.
Other subterranean locating techniques, for example, for locating adjacent wellbores, may include using driving electric current. U.S. Pat. No. 7,812,610 to Clark et al. discloses a method for locating well casings from an adjacent wellbore. More particularly, Clark et al. discloses a wellbore tool for locating a target wellbore containing a conductive member from a second wellbore and directing the trajectory of the second wellbore relative to the target wellbore. The wellbore tool includes an electric current driver having an insulated gap and at least one magnetometer positioned above or below the electric current driver. The electric current driver generates an electric current across the gap to the portions of the tool above and below the insulated gap.
Further improvements to mapping or tracking in a subterranean formation may be desirable. For example, it may be desirable to more quickly and easily map a wormhole, to more quickly repair a well and increase hydrocarbon resource recovery, for example.